1. Field of the Invention
The present invention relates to a technique of generating a higher-quality image by performing image processing to reduce blurs resulted from lens aberrations.
2. Description of the Related Art
Image degradation is known to occur when an object image captured by an image input apparatus such as a digital camera blurs more than actual due to the influence of aberrations of the lens and the like. A technique using the PSFs (Point Spread Functions) of an optical system is known as a technique of recovering the image quality by image processing (patent reference 1 (Japanese Patent Laid-Open No. 2001-197354) and patent reference 2 (Japanese Patent No. 03532368)). The technique using PSFs obtains a function (recovery function) for recovery based on a PSF and performs recovery processing using the recovery function. In this recovery processing, the PSF varies in accordance with the conditions of the lens type, the aperture, the focal length, the distance to the object, and the image height (the position from the optical axis center). In patent reference 1, PSFs corresponding to the respective conditions are held in advance and acquired upon image capturing to perform recovery processing. In patent reference 2, PSFs are held on concentric circles from the optical axis center and switched based on the image height of a captured image, thereby executing recovery processing.
The recovery processing will be described. Let o be the object, p be the PSF of a lens or the like, and n be noise. A captured image s obtained by an image input apparatus is expressed ass=o*p+n where “*” represents convolution. Obtaining a recovery filter r allows to derive an object o′ byo′=r*s 
At this time, r is the filter associated by p and n.
In the related art, however, the enormous data amount of PSFs and the large calculation amount pose a problem. As described above, the PSF varies depending on the position in an image. Hence, for image recovery on the entire screen, it is necessary to hold PSFs for the respective positions on the whole screen. In this case, the data amount of the PSFs becomes enormous, resulting in difficulty in PSF data exchange between the lens and the camera. When a PSF is held for each concentric region, as in patent reference 2, the region boundaries pose a problem. In addition, the PSF characteristics vary depending on not only the distance from the optical axis center but also the position with reference to the optical axis center. For this reason, the concentric regions do not suffice.
On the other hand, when holding the PSFs and calculating recovery filters from the PSFs at the time of image capturing, as in patent references 1 and 2, processing such as Fourier transformation in high calculation cost is necessary, resulting in a large calculation amount.